1. The Field of the Invention
The present invention relates to optical transceiver modules for use in optical communication networks. More specifically, the present invention relates to using a laser driver with signal conditioning capability as a component of the transceiver to control laser current characteristics and to improve the optical eye pattern quality associated with data signals generated by the laser.
2. The Related Technology
In the field of data transmission, one method of efficiently transporting data is through the use of fiber optics. Digital data is propagated through a fiber optic cable using light emitting diodes or lasers. Light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interferences that would otherwise interfere with electrical signals. Light signals are more secure because they do not allow portions of the signal to escape from the fiber optic cable as can occur with electrical signals in wire-based systems. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper wire.
Light signals are transmitted and received using transceivers, which include a transmitting component, or transmitter, having a laser and laser driver and a receiving component, or receiver, having a photodetector, a pre amplifier and a post amplifier. The transmitting component of the transceiver receives electrical signals representing network or communication data and processes the electrical signals to achieve the result of modulating the network or communication data onto an optical signal generated by the laser driver and the associated laser. The receiving component of the transceiver receives an optical signal from an optical fiber and converts the optical signal to an electrical signal that is used by an electronics or computing device connected with the transceiver.
Conventional transceivers include a separate post-amplifier and laser driver that are controlled using analog control signals sent by a controller component. The control signals are used for various purposes, most of which relate to adjusting the operation of the laser or the receiver in response to variations in the temperature of those components. The use of analog control signals has generally limited the number of separate parameters that can be controlled, since each separate controllable parameter associated with the operation of the receiver or transmitter requires a separate electrical connection used for transmission of a separate control signal associated with the controllable parameter. The use of multiple analog signals becomes increasingly difficult as the number of controllable parameters grows, particularly in view of the trend toward smaller transceivers. Thus, the use of analog control signals creates added complexity and expense to the design and manufacture of the transceiver PCB, while requiring each IC to be larger in size.
Lasers are used to encode data in an optical signal by representing digital bits of data as “1's” and “0's” that correspond to the presence or absence of the laser light. During recent years, data transmission rates in optical networks have increased, and conventional optical networks operate at 2.5 Gigabits (“Gbits”)/second or higher. As the data transmission rates increase, the characteristics of the laser operation in response to a signal from the laser driver to turn on or off become increasingly important. In general, lasers used in optical networks respond more quickly to a signal to turn on (e.g., application of a current that excites electrons and causes the emission of photons) than to a signal to turn off (e.g., removal of the current). As a result, the eye pattern, which represents the quality of the optical data signal, can deteriorate at high data transmission rates and can become a limiting factor associated with the maximum data rates that can be achieved with a given laser.
There is therefore a need for an optical transceiver that enables control over the various operational parameters of the transceiver components while minimizing the complexity and cost of the transceiver. In particular, a need exists for an optical transceiver that is capable of controlling laser operation such that modulation of a data signal is optimized, especially in high-speed optical networks.